The present invention relates to a seal for a rotating shaft and its housing. More particularly, it relates to the bearing isolator seal that uses a floating ring to seal stationary and rotating components.
Pumps, turbines, and electric motors contain shafts that rotate at a relatively high speed. The shafts are supported by at least one bearing to reduce friction. In these machines it is necessary to seal the space between the housing and the rotating shaft to prevent contaminants such as abrasive particles, moisture, or corrosive media from entering the bearing. A seal that performs such a task is traditionally referred to as a bearing isolator seal. Over the years, various types of seals have been developed to protect bearings. These include lip seals, labyrinth seals, magnetic seals, and brush seals.
The most commonly used and least expensive bearing isolator seal is the lip seal. A lip seal has a flexible leg pressed against the surface of the rotating shaft. Labyrinth seals have grooves in seal rings that impose a tortuous path that inhibits entry of contaminants into the bearing. An improved labyrinth seal that contains porous elements in the pathway to prevent the ingress of contaminated material is taught by Borowski in U.S. Pat. No. 5,480,161. Magnetic sealing systems rely on magnetic forces to maintain seal closure. Closure integrity can be maintained by magnetic attraction as in U.S. Pat. No. 4,795,168 or by magnetic repulsion as taught by Orlowski and Bloch in U.S. Pat. No. 5,161,804. Another type of seal is the brush seal, which is well suited for use with shafts that rotate at relatively high speed. Brush seals may have a variety of configurations. In a conventional configuration, bristles contact the rotating shaft and are flexible enough to allow the shaft to rotate but still maintain a seal while their holder is fixed to a stationary support holder. There are brush seal designs in which the brush or brushes are allowed to float as taught by Braun and Chey in U.S. Pat. No. 6,244,599.
Bearing life is shortened by bearing corrosion, which is caused by moisture and/or corrosive media. The prior art of bearing isolator seals is somewhat flawed because of potential problems with either sealing out moisture or corrosive media (identified with labyrinth or brush types) or with running dry or under too little lubrication (identified with lip or magnetic types). Lip type and magnetic type seals are contact seals that exclude contaminants well but require lubrication at seal contacting faces. A standard bearing lubrication system is not designed to provide lubrication for the bearing isolator seal.
The present invention is a contact type bearing isolator seal. Its novel features include a floating ring between a stationary retainer ring and a mating ring that rotates with a shaft. The floating ring is made of a material with a low coefficient of friction and a low elastic modulus such as polytetrafluoroethylene (PTFE) or graphite/PTFE composite. The floating ring can have several cross-sectional shapes, e.g. Z-shaped, U-shaped, and V-shaped.